Increasingly at present, hydraulic power is being used to drive and control heavy machinery such as loaders and digging machines. The use of hydraulic power has considerable advantages in wear, controllability et cetera.
Because heavy machinery is becoming large, larger and larger hydraulic drive pumps are now required. For example, cog-wheel pumps are used because they are fabricated at low cost relative to their large capacity. Cog-wheel pumps and other pumps unfortunately, however, do not deliver an absolutely even flow. Pulsations, vibrations, shocks and even blows occur. Blows are particularly prevalent when very high pressures are used. The resulting vibration and noise are disturbing for the driver, disturbing for the environment, and increase strain on the machine.
A possible way to solve this problem is to provide pulsation equalizers. Pulsation equalizers which can handle very high hydraulic pressures are, however, very expensive. The working pressures encountered in heavy machinery can be as high as 200 kp/cm.sup.2. In addition, a single piece of heavy machinery may require damping the vibration of two or three pumps. Multiple expensive pulsation equalizers would then be required.